why is a shottky diode used in the circuit

[vasudhaptx]

Hi,

CAn any one help me understand why is the schottky diode (marked in red ) used in the circuit. Please help

 

[IanP]

It doesn't need to be Schottky dual-diode, it can be any small-signal fast silicone diode pair ..
Someone just have two diodes in a single package and it happend to be Schottky - convenience perhaps ..

Rgds,
IanP

 

[vasudhaptx]

Hi ,

thanks for the reply. But can you tell me how will the usage of those diodes help?. wht will happen if those diodes are not used at all?. Is it for voltage clamping? If yes please explain.

Regards
Vasudha

 

[IanP]

These two diodes protect the output pin from external over- or under-voltages ..
As you can see one diode is connected between pin and Vcc, it claps voltages at Vcc+0.5V (depending on the Vf of the diode), the second diode is connected between pin and GND, it claps voltages at GND-0.5V = -0.5V ..
If the output is not exposed to voltages beyond GND(-0.5) and Vcc(+0.5) it’s possible that they will never act as protection .. they will be just sitting there doing nothing ..

And one more thing, if the IC pin can not tolerate voltages above Vcc+0.5V and Vdd-0.5V these protective diodes have to be of Schottky type, as for standard silicone diodes the forward voltage is roughly 0.7V ..

Rgds,
IanP

 

[vasudhaptx]

that was very helpful. thank you

regards
Vasudha